Lubricant Compositions

ABSTRACT

Disclosed is a lubricant composition for use in association with a device involving metal-to-metal contact of moving parts, the composition comprising (a) a base stock comprising at least one low viscosity poly-alpha-olefin; (b) a viscosity improver comprising at least one high viscosity poly-alpha-olefin; and (c) a performance additive comprising at least one compound effective to improve at least one property of the lubricant and/or the performance of the equipment in which the lubricant is to be used.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 13/121,121, filed on Sep. 16, 2009, which is the National Stage entry of PCT/EP09/06681, filed on Sep. 16, 2009, which claims priority to U.S. Provisional Application No. 61/100,255, filed on Sep. 25, 2008, all of which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

This invention relates to lubricant compositions having utility in numerous applications, particularly in connection with gear, transmission and/or axle applications in the automotive and machinery industries. In preferred aspects, the present invention is directed to lubricant compositions having particular advantages as axle fluids, and more particularly as heavy duty axle fluids.

BACKGROUND OF THE INVENTION

An important function of lubricant compositions, and in particular, gear and axle lubricant fluids, is to provide a high degree of reliability and durability in the service life of equipment in which it is installed. With the increasing costs of energy, particularly gasoline and diesel fuel, the ability of such lubricants to aid in the overall fuel economy of the vehicles in which they are used has become an increasingly important factor in the selection of gear and axle lubricants. Applicants have come to appreciate that by improving the axle efficiency, particularly in heavy duty applications such as Class 8 line haul trucks and vocational vehicles, the fuel efficiency of the vehicles can be improved.

Lubricating oils in general, and gear and axle lubricants in particular, must satisfy a large number of performance criteria to be commercially successful. For example, a commercially successful axle lubricant will frequently be required to possess a high degree of oxidative stability, compatibility, shear stability, corrosion avoidance or resistance, wear protection, shiftability, and extended drain. These properties represent a difficult-to-achieve set of performance criteria that is made all the more difficult to achieve if the requirement of enhancing fuel efficiency is also added.

BRIEF SUMMARY OF THE INVENTION

Applicants have developed improved lubricant compositions, and in many embodiments lubricant compositions, that satisfy at a high level of performance, many, and preferably all, of the criteria mentioned above. As used herein, the term “lubricant composition” is used in its broadest sense to include fluid compositions that are used in applications involving metal-to-metal contact of parts in which at least one function of the fluid is to inhibit or reduce friction between the parts. As such, the term “lubricant composition”, as used herein, includes gear oils, axle oils and the like.

Preferably the lubricant compositions of the present invention comprise (a) basestock; (b) viscosity improver; and (c) at least one additive to inhibit, and preferably substantially prevent, one or more of wearing, scuffing, micropitting and combinations of these and other deleterious effects. In preferred embodiments the lubricant compositions of the present invention comprise (a) basestock comprising poly-alpha-olefin (hereinafter referred to as “PAO”), preferably low viscosity PAO, and even more preferably a PAO having a viscosity of not greater than about 12 centistokes (cSt), and optionally an ester oil; (b) viscosity improver comprising at least one high viscosity PAO-type viscosity improver, preferably having a viscosity of greater than about 40 centistokes (cSt), and even more preferably from about 40 to about 1000 cSt; and (c) a performance additive package comprising at least one additive effective to improve at least one property of the lubricant and/or the performance of the equipment in which the lubricant is to be used. In certain preferred embodiments, the performance additive comprises at least one sulfur-containing compound and at least one phosphorous-containing compound.

Applicants have found that preferred lubricant compositions of the present invention exhibit and/or produce one or more, and preferably all, of the following advantageous properties: reduction of viscous drag over the application temperature range; film thickness reduction; and churning loss reduction.

In preferred embodiments, the present lubricant compositions exhibit a horsepower (HP) loss reduction, as described and measured in connection with the examples hereof, of at least about 3%, more preferably at least about 4%, and even more preferably at least about 5%.

In preferred embodiments, the present lubricant compositions exhibit a sump temperature reduction, as described and measured in connection with the examples hereof, of at least about 2%, more preferably at least about 5%, and even more preferably at least about 7%.

Other embodiments of the present invention are directed to methods of making and using a fully formulated lubricant, including a fully formulated heavy duty axle fluid. A final embodiment of the invention is directed to axle, gear, transmission and/or drive systems containing such oils.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 displays pictures of gear components illustrating the sludge control properties of a lubricant composition of the invention versus standard lubricants.

FIG. 2 shows a graph of frictional properties of lubricant compositions of the invention versus standard lubricants.

FIG. 3 shows a schematic diagram of a test apparatus for evaluating frictional properties of a lubricant composition.

FIG. 4 shows a graph of traction properties of lubricant compositions of the invention versus standard lubricants.

FIG. 5 shows a schematic diagram of a test apparatus for evaluating the traction properties of a lubricant composition.

FIG. 6 shows a graph of the seal compatibility properties of lubricant compositions of the invention versus standard lubricants.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed in one aspect to lubricant compositions comprising at least one base stock, at least one viscosity enhancer for the base stock, and at least one additive. In general, it is contemplated that these components of the present invention may be present in the compositions in widely varying amounts depending on the particular needs of each application, and all such variations are considered to be within the broad scope of the invention. Nevertheless, applicants have found that in certain preferred embodiments, the present lubricant compositions are formulated according to the following preferred ranges of components, it being understood that all percentage values indicated in Table 1 are modified by the word “about”.

TABLE 1 Broad Intermediate Narrow Wt % Range Wt % Range Wt % Range Basestock 10-90  15-80  15-60  Viscosity 2-70 5-60 5-60 Improver Additive 2-30 5-20 5-15

With respect to certain preferred embodiments, the base stock comprises at least one low viscosity PAO and at least one adipate ester. While it is contemplated that a wide range of relative concentrations of such components may be present, in general it is preferred that the base stock of the present invention comprise in certain embodiments a PAO:ester weight ratio of from about 0.5 to about 12:1, and more preferably of from about 0.5 to about 12:1. In certain embodiments it is also preferred that the viscosity improver comprise a high viscosity PAO (hereinafter HVPAO) and an additional additive selected from the group consisting of PIB (polyisobutylene), PMA (polymethacrylate), or OCP (olefin co-polymer), and combinations of two or more of these. While it is contemplated that a wide range of relative concentrations of such components may be present, in general it is preferred that the viscosity enhancer of the present invention comprise in certain embodiments an additional additive:HVPAO weight ratio of from about 0 to about 4:1, and more preferably of from about 0.2 to about 4:1.

Applicants have found that in certain preferred embodiments the present lubricant compositions are formulated according to the following preferred ranges of components, it being understood that all percentage values indicated in Table 2 are modified by the word “about”.

Although it is contemplated that the PAO used in connection with the base stock component of the present invention may vary widely in particular properties and/or structures, in certain embodiments the PAO component is a PAO having a viscosity of from about 4 to about 12 cSt. In preferred embodiments the PAO is selected from group consisting of PAOs having a viscosity of about 4, 6, 8, 10, 12 or combinations of two or more of these. In certain preferred embodiments, the PAO used in connection with the base stock component of the present invention is comprised of oligomeric compounds having from 2 to about 3 units, preferably units of 1-decene.

Although it is also contemplated that the PAO used in connection with the viscosity enhancer component of the present invention may vary widely in particular properties and/or structures, in certain embodiments the PAO component of the viscosity enhancer comprises, and preferably in certain embodiments consists essentially of a PAO having a viscosity greater than about 40 cSt, and even more preferably from about 40 to about 1000 cSt. In preferred embodiments, the PAO component of the viscosity enhancer is comprised of polymeric compounds having greater than about 50 units, more preferably having greater than about 75 units and even more preferably having greater than about 100 units, preferably units of 1-decene.

TABLE 2 Broad Intermediate Narrow Wt % Range Wt % Range Wt % Range Basestock -  2-30  5-30  5-20 adipate ester Basestock - 10-70 10-60 10-40 PAO (preferably 4-12 cSt or 6-8 cSt) Viscosity  2-50  5-50  5-40 Improver - HVPAO Additive -  0-30  0-25  0-20 ANGAMGL ® 6004j or GL-4 Gear Oil package Additive - PMA 0-3 0-2 0-1 Additive - 0-3 0-2 0-1 Defoamer (silicone based)

Applicants believe that, in general, numerous particular compounds or combinations of compounds are available for use in connection with each of the ingredients as described herein. With respect to the optional adipate ester, it is preferred in certain embodiments that the adipate ester comprises a decyl adipate, and even more particularly, of one or more adipate esters selected from the group consisting of di-isodecyl adipate, and di-tridecyl adipate. In a further embodiment, the preferred ester comprises di-isodecyl azelate.

In certain preferred embodiments, the present lubricant compositions are formulated in accordance with Tables 3 or 4 below, it being understood that the amounts are weight percentages and the each value is understood to be preceded by the word “about”.

TABLE 3 Basestock adipate 5-20% Basestock Low Viscosity PAO (4-12 cSt) 20-60% Thickener PAO 40-1000 5-40% Thickener PIP, PMA or OCP 0-20% Adpack GL-4 Gear Oil Package 5-15% PPD PMA Polymer 0-2.0% Defoamer Silicone based 0-2.0%

TABLE 4 Basestock di-isodecyl adipate 5-20% Basestock Low Viscosity PAO (6-8 cSt) 10-40% Thickener PAO 40-100 5-40% Thickener PIP or OCP 0-20% Adpack ANGAMOL ® 6004J 5-15% PPD PMA Polymer 0-1.0% Defoamer Silicone based 0-1.0%

EXAMPLES

The following examples are provided for the purpose of illustrating the present invention but without limiting the scope thereof.

Average Horsepower Loss Comparative Examples C1-C4 and Examples E1-E4

The average horsepower loss (“AHPL”) is one measure that can be used to represent the performance of a lubricant composition, particularly an axle or gear oil, with respect to the fuel economy impact on the vehicle in which it will be used. In order to obtain information regarding the relative performance of certain preferred lubricants in accordance with the present invention, a testing protocol is used in which a commercial axle is attached to a dynamometer which es the input and the output torque on the axle. This test is run for comparison purposes with several commercially available lubricants and also with two formulations in accordance with the preferred embodiments of the present invention. In order to help assess the relative performance of the different lubricant formulations, a commercially available product sold under the trade designation EMGARD® 2986 is tested several times (identified with row headings C1A-C1F) in order to establish an average value for comparison purposes, which values are reported at the end of Table 5. The results of the test done in connection with the commercially available products are identified across the row headings C1-C4 in Table 5. The results of the tests performed in connection with four lubricant compositions of the present invention are reported-as E1-E4.

TABLE 5 Ending Sump Sump Hp Loss Temp Average Temp Reduc- Reduc- Hp Loss (C.) tion % tion % C1A -EMGARD ® 2.924 82.5 −0.5% −1.4% 2986 E1 -Cognis 3 2.847 80.6 2.1% 0.9% (704-156-4 E2 - 100 cSt PAO 2.750 77.0 5.45 5.3% (770-11-11) C1B -EMGARD ® 2.891 84.6 0.6% −4.0% 2986 C1C -EMGARD ® 2.894 80.5 0.5% 1.1% 2986 C2 -EMGARD ® 4209 2.893 80.3 0.5% 1.3% Aged (770-26-2) C3 - Q8 (188-185) 2.841 77.2 2.3% 5.1% C1D -EMGARD ® 2.930 80.1 −0.7% 1.5% 2986 E3 -PAO100/PIB/PA08 2.800 76.6 3.7% 5.9% (770-39-1) E4 -PAO100/PA06 2.783 75.2 4.3% 7.5% (770-42-1) C4 -LUCANT ® 2.917 80.2 −0.3% 1.4% 600/PA08 (770-35-7) C1F -EMGARD ® 2.907 80.1 0.1% 1.5% 2986 EMGARD ® 2.908 81.3 2986 (ave) EMGARD ® 2.908 81.3 2986 (ave) EMGARD ® 0.016 1.836 2986 (stdev) EMGARD ® 0.54% 2.26% 2986 (% dev)

As can be seen from Table 5, the lubricant composition in accordance with the present invention labeled E2 exhibited a 5.4% relative improvement in energy efficiency compared to the average established for EMGARD® 2896. The formulation designated as E2 in Table 5 consisted essentially of (CAS #770-11-11) di-isodecyl adipate (5%). PAO 8 (56.6%). PAO 100 (28%). ANGAMOL® 6004J (10%), HiTEC 5739 (0.3%), E-9817U (0.1%), with all amounts being reported on the basis of weight percent. Also as can be seen from Table 5 above, the lubricant composition in accordance with the present invention labeled E3 exhibited a 3.7% relative improvement in energy efficiency compared to the average established for EMGARD® 2896. The formulation designated as E3 in Table 5 consisted essentially of (CAS #770-39-1) di-isodecyl adipate (5%), PAO 8 (56.6%), PAO 100 (13%), INDOPOL® H-1500 SPA (13%), ANGAMOL® 6004J (10%), HiTEC 5739 (0.3%), E-9817U (0.1%), with all amounts being reported on the basis of weight percent. And finally, the lubricant composition in accordance with the present invention labeled E4 exhibited a 4.3% relative improvement in energy efficiency compared to the average established for EMGARD® 2896. The formulation designated as E4 in Table 5 consisted essentially of (CAS #770-42-1) di-isodecyl adipate (5%), PAO 8 (51.6%), PAO 100 (33%), ANGAMOL® 6004J (10%), HiTEC 5739 (0.3%), and E-9817U (0.1%), with all amounts being reported on the basis of weight percent.

Physical Properties Comparative Examples C1, C5, C6 and C7 and Examples Cognis #2 and Cognis #3

Several properties exist which, at least in certain applications, are considered relevant to the effectiveness of lubricant compositions. Tests are performed for the purpose of obtaining information regarding the relative performance of certain preferred lubricants in accordance with the present invention relative to several commercially available lubricants. The results of the test done for comparison purposes in connection with the commercially available products are identified under column headings EMGARD® 4209, EMGARD® 2986, Comp Q and Comp S in Table 6. The results of the tests performed in connection with two lubricant compositions of the present invention are based on the same formulation reported in Table 5 as E1 and E2, but labeled in Table 6 with row headings Cognis #2 and Cognis #3, respectively.

Based upon the results reported in Table 6, it is seen that the lubricant compositions in accordance with the present invention exhibit excellent shear stability and low temperature properties relative to leading commercially available axle lubricants.

Corrosion and Anti-Wear Properties Comparative Examples C1, C5, C6 and C7 and Examples Cognis #2 and Cognis #3

Several properties exist which, at least in certain applications, are considered relevant to the anti-corrosion and anti-wear abilities of lubricant compositions. Several tests are performed for the purpose of obtaining information regarding the relative performance of certain preferred lubricants in accordance with the present invention relative to several commercially available lubricants. The results of the test done for comparison purposes in connection with the commercially available products are identified under column headings EMGARD® 4209, EMGARD® 2986, Comp Q and Comp S in Table 7. The results of the tests performed in connection with two lubricant compositions of the present invention are based on the same formulation reported in Table 5 as E1 and E2, but labeled in Table 7 with row headings Cognis #2 and Cognis #3, respectively.

Based upon the results reported in Table 7, it is seen that the lubricant compositions in accordance with the present invention exhibit excellent corrosion resistance and wear resistance properties.

Stability Comparative Examples C1, C5, C6 and C7 and Examples Cognis #2 and Cognis #3

Several properties exist which, at least in certain applications, are considered relevant to the stability of lubricant compositions in the environment of use. Several tests are performed for the purpose of obtaining information regarding the relative performance of certain preferred lubricants in accordance with the present invention relative to several commercially available lubricants. The results of the test done for comparison purposes in connection with the commercially available products are identified under column headings EMGARD® 4209, EMGARD® 2986, Comp Q and Comp S in the Table 8. The results of the tests performed in connection with two lubricant compositions of the present invention are based on the same formulation reported in Table 5 as E1 and E2, but labeled in Table 8 with row headings Cognis #2 and Cognis #3, respectively.

Based upon the results reported in Table 8, it is seen that the lubricant compositions in accordance with the present invention exhibit excellent stability.

Sludge Control Comparative Examples C1, C5, C6 and C7 and Examples Cognis #2 and Cognis #3

Several properties exist which, at least in certain applications, are considered relevant to the ability of lubricant compositions to have a positive effect on the control of sludge creation and/or build up in the environment of use. Several tests are performed for the purpose of obtaining information regarding the relative performance of certain preferred lubricants in accordance with the present invention relative to several commercially available lubricants. The results of the test done for comparison purposes in connection with the commercially available products are identified under column headings EMGARD® 4209, EMGARD® 2986, Comp Q and Comp S in the Table 9, and associated FIG. 1. The results of the tests performed in connection with two lubricant compositions of the present are based on the same formulation reported in Table 5 as E1 and E2, but labeled in Table 9 with row headings Cognis #2 and Cognis #3, respectively.

Based upon the results reported in Table 9 and FIG. 1, it is seen that the lubricant compositions in accordance with the present invention exhibit excellent sludge control.

Wear Control Comparative Examples C1, C5, C6 and C7 and Examples Cognis #2 and Cognis #3

Several properties exist which, at least in certain applications, are considered relevant to the ability of lubricant compositions to resist or reduce the rate of wear of the moving metal parts with which it is in contact in the environment of use. Several tests are performed for the purpose of obtaining information regarding the relative performance of certain preferred lubricants in accordance with the present invention relative to several commercially available lubricants. The results of the test done for comparison purposes in connection with the commercially available products are identified under column headings EMGARD® 4209, EMGARD® 2986, Comp Q and Comp S in the Table 10. The results of the tests performed in connection with two lubricant compositions of the present invention are based on the same formulation reported in Table 5 as E1 and E2, but labeled in Table 10 with row headings Cognis #2 and Cognis #3, respectively.

Based upon the results reported in Table 10, it is seen that the lubricant compositions in accordance with the present invention exhibit excellent wear resistant properties.

Frictional Properties Comparative Examples C1, C5, C6 and C7 and Examples Cognis #2 and Cognis #3

The frictional properties of a lubricant composition are in general considered to be highly relevant to the ability of lubricant compositions to exhibit superior performance in the environment of use. Several tests are performed for the purpose of obtaining information regarding the relative performance of certain preferred lubricants in accordance with the present invention relative to several commercially available lubricants. The results of the test done for comparison purposes in connection with the commercially available products are identified under column headings EMGARD® 4209, EMGARD® 2986, Comp Q and Comp S in FIG. 2. The results of this test in accordance with the present invention are based on the same formulation reported in Table 5 as E1 and E2, but labeled in FIG. 2 as Cognis #2 and Cognis #3, respectively

One method of testing the frictional properties of lubricant is to utilize a 19.05 mm (¾ inch) steel ball and 46 mm diameter steel desk. The ball is loaded against the face of the disc and the ball and the disc are driven independently to create a mixed rolling/sliding contact. The force between the ball and disk is measured by a force transducer. Additional sensors measure the applied load, the lubricant temperature and (optionally) electrical contact resistance between specimens and the relative wear between them. A schematic diagram of such a test apparatus is provided in FIG. 3.

Such an apparatus is used to test lubricant compositions in accordance with the present invention, using a film thickness of one to 1000 nm (±1 nm), speeds of 0.010-1.0 m/s, loads of 100 N, a slide/roll ratio (SSR) of 50%, contact pressures of up to approximately 3.0 GPa, a temperature range of from 40 to 100° C., a power supply of from 100 to about 240 V, a total weight of 50 kg and dimensions (W×H×D) of 50×50×30 cm. The results of this test indicate that lubricant compositions in accordance with preferred aspects of the present invention produce exceptionally low friction coefficients relative to other commercially available lubricant compositions, as identified in FIG. 2.

Traction Properties Comparative Examples C1, C5, C6 and C7 and Examples Cognis #2 and Cognis #3

The traction properties of a fluid in many instances are relevant to the ability of lubricant compositions to exhibit superior performance in the environment of use. Several tests are performed for the purpose of obtaining information regarding the relative performance of certain preferred lubricants in accordance with the present invention relative to several commercially available lubricants. The results of the test done for comparison purposes in connection with the commercially available products are identified under column headings EMGARD® 4209, EMGARD® 2986, Comp Q and Comp S in FIG. 4. The results of the tests performed in connection with two lubricant compositions of the present invention are based on the same formulation reported in Table 5 as E1 and E2, but labeled in FIG. 4 as Cognis #2 and Cognis #3, respectively.

One method of testing the traction properties of a lubricant composition is to measure the thickness and traction properties of elastohydrodynamic lubricant (EHL) films utilizing an apparatus having at least one bowl or roller loaded against the internal diameter of a transparent ring having a larger radius than the bowl or roller. The lubricant to be tested is placed between the rotating roller and arraying thereby forming an EHL film where the ball and arraying contact. Roller and arraying rotating speeds are controlled to obtain different amounts of relative sliding motion between the respective surfaces. Contact between the surfaces and the resultant film are observed by way of a transparent ring which allows optical measurements of lubricating film thickness. Traction forces generated during contact are also measured. A schematic diagram of such a test apparatus is provided in FIG. 5.

Such an apparatus is used to test lubricant compositions in accordance with the present invention, using a film thickness of one to 1000 nm (±1 nm), speeds of 0.010-3.5 m/s, loads of 1 to 50 N, a slide/roll ratio (SSR) of 50%, contact pressures of up to approximately 3.0 GPa, a temperature range of from 40 to 100° C., a power supply of from 100 to about 240 V, a total weight of 50 kg and dimensions (W×H×D) of 50×50×30 cm. The results of this test indicate that lubricant compositions in accordance with preferred aspects of the present invention produced acceptable film thicknesses, especially at temperatures of 40° C., relative to other commercially available lubricant compositions, as identified in FIG. 4.

Seal Compatibility Comparative Examples C1, C5, C6 and C7 and Examples Cognis #2 and Cognis #3

One property of lubricant compositions which is considered to be important, at least in certain applications, is the compatibility of the lubricant with nonmetal parts in the system and environment of use, especially including seals, gaskets and the like. Several tests are performed for the purpose of obtaining information regarding the relative performance of certain preferred lubricants in accordance with the present invention relative to several commercially available lubricants in connection with seal compatibility. The results of the test done for comparison purposes in connection with the commercially available products are identified under column headings EMGARD® 4209, EMGARD® 2986, Comp Q and Comp S in Table 11 and FIG. 6. The results of the tests performed in connection with two lubricant compositions of the present invention are based on the same formulation reported in Table 5 as E1 and E2, but labeled in Table 11 with row headings Cognis #2 and Cognis #3, respectively.

Based upon the results reported in Table 11 and the associated graph, FIG. 6, it is seen that the lubricant compositions in accordance with the present invention exhibit, or would be expected to exhibit, excellent compatibility with the seals, gaskets and the like, used in connection with the systems and devices in which the present lubricant compositions are intended to be included.

TABLE 6 PHYSICAL PROPERTIES OF LUBRICANT COMPOSITIONS, Physical EMGARD ® EMGARD ® Cognis Cognis Comp Comp Properties 4209 2986 #2 #3 Q S Kinematic ASTM 16.8 15.0 14.5 14.83 14.59 14.59 Viscosity D445 @ 100° C., cST Kinematic ASTM 115 103.0 95.45 100.25 94.73 93.55 Viscosity @ D445 40° C., cST Kinematic ASTM 115,000 92,000 83,000 130,500 161,200 168,000 Viscosity @ D445 −40° C., cSt Brookfield ASTM 186,000 90,000 68,000 62,000 121,300 82,200 Viscosity @ D2983 −40° C., cP Viscosity Index ASTM 160 152 158 154 160 154 (calculated) D2270 Viscosity Shear CEC L- 9.98 10.38 11.59 1.50 6.12 9.59 Loss, 60 h 45-A-99 Channel Point, FTMS- −45 −45 −45 −45 −45 −45 ° C. 3456.2 Pour Point, ° C. ASTM −50 −57 −45 −45 −45 −51 D97 Flash Point, ° C. ASTM 220 215 210 210 218 207 D92 Specific Gravity, ASTM 0.863 0.891 0.8573 0.8531 0.8607 0.8733 15.6° C. D4052 Density, g/L ASTM 863 891 856 853 868 872 @ 15.6° C. D1298

TABLE 7 CORROSION AND ANTI-WEAR PROPERTIES OF LUBRICANT COMPOSITIONS. EMGARD ® EMGARD ® Cognis Cognis Comp Comp 4209 2986 #2 #3 Q S Foam Test ASTM D892 Sequence I 0/0 0/0 0/0 0/0 20/0  0/0 Sequence II 10/0  50/0  0/0 0/0 270/0  100/0 Sequence III 0/0 0/0 0/0 0/0 20/0  0/0 Copper Strip ASTM D130 Corrosion 3 hrs @ 121° C. 1b 1a 1a 1b 2e 3a Four Ball EP ASTM D2783 Load-Wear 77.0 83.7 72.0 78.0 69.8 62.2 Index, kgf 400 500 400 400 315 400 Weld Point, kg Four Ball ASTM D4172 Wear Scar Diameter, 0.44 0.74 0.42 0.43 0.53 0.57 mm FZG, Step acc. FVA-243 >10 >10 >10 >10 Load (Sprung) S- (est) (est) Test, stage A10/16.6R/90

TABLE 8 STABILITY PROPERTIES OF LUBRICANT COMPOSITIONS. EMGARD ® EMGARD ® Cognis Cognis Comp Comp 4209 2986 #2 #3 Q S Oxidation DKA CEC L- (192 hrs., 160° C.) 48-A-00 Fresh Kinematic ASTM 16.87 14.97 14.65 14.92 14.44 14.52 Viscosity @ D445 100° C., cST Kinematic ASTM 117.3 103.46 96.99 97.73 93.3 105.33 Viscosity @ 40° C., D445 cSt TAN CEC L- 2.4 1.92 2.5 1.72 1.39 2.17 48-A-00 Aged Kinematic ASTM 31.84 26.28 22.09 18.95 20.46 24.81 Viscosity @ D445 100° C., cST Kinematic ASTM 261.9 202.73 161.9 132.75 139.54 207.42 Viscosity @ 40° C., D445 cSt TAN, mgKOH/g ASTM 5.8 4.03 5.1 2.11 2.62 6.68 D664 PAI (peak area CEC L- 143.9 18.70 100.3 17.59 26.94 41.57 increase) 48-A-00 Sludge Rating, CEC L- 3 1 2 3 3 1 Aspect 48-A-00 Dispersancy 86 (blotter test) Variation Variation 88.7 75.6 50.8 27.0 41.7 70.9 Kinematic Vis. @ 100° C., % Variation 123.3 96.0 66.9 35.8 49.6 96.9 Kinematic Vis. @ 40° C., % Variation TAN, 3.4 2.1 2.6 0.39 1.2 4.5 mgKOH/g

TABLE 9 SLUDGE CONTROL PROPERTIES OF LUBRICANT COMPOSITIONS. EMGARD ® EMGARD ® Cognis Cognis Comp Comp 4209 2986 #2 #3 Q S Oxidation L-60-1 ASTM (200 hrs, 163° C.) D5704 Viscosity 37.5 (50 h) 93 75.1 23.8 67.3 Increase, % C/V Rating, merit 9.55 (50 h) 9.1 9.0 1.5 8.5 Sludge Rating,  9.5 (50 h) 9.6 9.0 1.5 8.5 merit

TABLE 10 WEAR CONTROL PROPERTIES OF LUBRICANT COMPOSITIONS. EMGARD ® EMGARD ® Cognis Cognis Comp Comp 4209 2986 #2 #3 Q S High Temperature ASTM Towing HT-L-37 D6121 Ring Gear Wear 8.0 7.0 7.0 5.0 Rippling 9.0 10.0 10.0 8.0 Ridging 10 10.0 10.0 5.0 Pitting/Spalling 9.9 9.9 10.0 8.0 Scoring 10 10.0 10.0 10.0 Pinion Gear Wear 8.0 7.0 7.0 4.0 Rippling 9.0 9.0 10.0 7.0 Ridging 10 9.0 9.0 4.0 Pitting/Spalling 9.9 9.9 10.0 8.0 Scoring 10 10.0 10.0 10.0

TABLE 11 SEAL COMPATIBILITY PROPERTIES OF LUBRICANT COMPOSITIONS. EMGARD ® EMGARD ® Cognis Cognis Comp Comp 4209 2986 #2 #3 Q S Thickness @ 40° C. (1.133 419 480 380 419 441 435 m/s), nm Thickness @ 100° C. 105 103 111 100 103 127 (1.133 m/s), nm 

What is claimed is:
 1. A method for operating Class 8 line haul trucks and vocational vehicles, comprising: (a) obtaining an axle fluid, the axle fluid comprising: i. basestock comprising at least one PAO having a viscosity in the range of about 4-12 centistokes, ii. a viscosity improver comprising at least one PAO having a viscosity in the range of about 40 to about 1000 centistokes, iii. an ester oil, and iv. optionally, a co-thickener performance additive; and (b) contacting an axle of a Class 8 line haul truck or vocational vehicle with the axle fluid.
 2. The method of claim 1, wherein the contacting step comprises contacting moving metal parts.
 3. The method of claim 2, wherein a horsepower loss reduction of at least about 3% is achieved.
 4. The method of claim 2, wherein a sump temperature reduction of at least about 2% is achieved.
 5. The method of claim 2, wherein improved fuel efficiency of the Class 8 line haul truck or vocational vehicle is achieved.
 6. The method of claim 1, wherein the axle fluid has a viscosity index in the range of 152-160.
 7. The method of claim 1, wherein the axle fluid further comprises, based on the composition, by weight: the basestock (a) in an amount in the range of about 10 to about 90%, the viscosity improver (b) an amount in the range of about 2 to about 70%, the ester oil (c) in an amount in the range of about 2 to about 30%, and performance additive (d) an amount in the range of about 2 to about 30%.
 8. The method of claim 7, wherein the axle fluid comprises, based on the composition, by weight: the basestock (a) in an amount in the range of about 15 to about 60%, the viscosity improver (b) in the range of about 5 to about 60%, the ester oil (c) in an amount in the range of about 5 to about 20%, and the performance additive (d) in an amount in the range of about 5 to about 15%.
 9. The method of claim 1, wherein said ester oil comprises at least one adipate ester.
 10. The method of claim 9, wherein said ester oil consists of one or more adipate esters selected from the group consisting of di-isodecyl adipate and di-tridecyl adipate, and is present in 2-30% by weight, based on the lubricant composition.
 11. The method of claim 1, wherein the axle fluid consists essentially of, based on the composition, by weight: the basestock (a) having a viscosity in the range of 6-8 centistokes in an amount in the range of about 15 to about 60%, the viscosity improver (b) having a viscosity in the range of 40-100 centistokes in the range of about 5 to about 60%, the ester oil (c) comprising diisodecyl adipate in an amount in the range of about 5 to about 20%, and the co-thickener (d) comprising a polyisobutylene (PIB), a polymethacrylate (PMA), or an olefin co-polymer (OCP) in an amount in the range of about 5 to about 15%.
 12. The method of claim 6, wherein a weight ratio of the at least one PAO having a viscosity in the range of about 4-12 centistokes to the ester oil is in the range of about 0.5:1 to about 12:1.
 13. The method of claim 6, wherein the axle fluid comprises: (a) a PAO having a viscosity of about 4-12 centistokes in an amount in the range of about 50 to about 60% by weight of the axle fluid, (b) a PAO having a viscosity of about 100 centistokes in an amount in the range of about 5 to about 40% by weight of the axle fluid, and (c) di-isodecyl adipate in an amount of about 5% by weight of the axle fluid. 